Microsoft Corp. today spelled out new privacy tools in Internet Explorer 8 (IE8) that some have dubbed "porn mode" in a nod to the most obvious use of a browser privacy mode.

A privacy advocate applauded the move, calling it a "great step forward," while rival browser builder Mozilla Corp. said it is working to add similar features to a future Firefox.

Slated to appear in IE8 Beta 2, which Microsoft former chairman Bill Gates promised will release this month, the three new tools share the "InPrivate" name, which Microsoft filed with the U.S. Patent and Trademark Office several weeks ago.

The most intriguing tool, and the one that has prompted the porn mode label, was called InPrivate Browsing by Microsoft. When enabled, IE8 will not save browsing and searching history, cookies, form data and passwords; it also will automatically clear the browser cache at the end of the session.

Other new tools will include InPrivate Blocking and InPrivate Subscription, which notifies users of third-party content that can track browsing history and subscribe to lists of sites to block, respectively. Microsoft will also tweak its existing "Delete Browsing History" by adding an option to preserve bookmarked sites' cookies even when all others are erased.

"When we began planning IE8, we took a hard look at our customers' concerns about privacy on the Web," said Andy Zeigler, an IE program manager, as he explained InPrivate Browsing in a long post to the team's blog. "Many users are concerned about so-called over-the-shoulder privacy, or the ability to control what their spouses, friends, kids and co-workers might see.

"If you are using a shared PC, a borrowed laptop from a friend or a public PC, sometimes you don't want other people to know where you've been," Zeigler added.

One wag commenting on Zeigler's post quoted some of his text before shooting back. "You know as well as I do this feature is built for porn," said a user identified as "Ert."

Instead, Mozilla has used the term "private browsing" to describe the tools it plans on adding to Firefox, perhaps in a follow-on to Firefox 3.1, which the company has targeted for a release later this year or in early 2009.

Mozilla's goal, however, is to offer more than a privacy mode that users must switch on before the browser begins to cover their tracks. "We want users to not only be able to enter [a private browsing session], but tell the browser that they want to delete all evidence starting a couple of hours ago," said Beltzner.

Firefox 3.0, which went final in mid-June, was meant to have a privacy mode similar to what Microsoft promised today for IE8, but the feature was pulled as the browser made its run toward completion. Beltzner wouldn't put a timetable on the enhancements, saying that he couldn't guarantee they would make it into Firefox 3.1.

Ari Schwartz, deputy director of the Center for Democracy and Technology (CDT), a nonprofit policy group in Washington, said moves such as Microsoft's are important, not because they are new technologies, but because they put tools in the hands of more Internet users.

"The key part is getting privacy tools into the browser," said Schwartz, "rather than as add-ons or extensions. Microsoft's announcement is significant not because it's a major technological breakthrough, but because it's a breakthrough into making it easier for users to have real control over their privacy."

The CDT, said Schwartz, has talked with every browser developer about adding more privacy features to their applications, and was happy to see progress. Of the most-used browsers, only Apple Inc.'s Safari currently has a privacy mode. "But we'll have to wait to see how easy it is to use," he cautioned, talking about IE8's InPrivate tools.

Beltzner, meanwhile, echoed Schwartz on the need for a more granular approach to browsing privacy and wondered if the tools would be used by mainstream surfers. They both noted that the problem exists on shared computers in places such as schools or Internet cafes. "What we're seeing in Firefox is that people want their browsers to remember more, not less," he said, citing the work Mozilla did on Firefox 3.0's location bar to add search capabilities so users could retrieve previously visited sites.

Microsoft has not set a date for IE8 Beta 2's release, saying only that it would unveil the browser before the end of August. Company executives have said that the final version of IE8 will launch sometime this year.